iBeacon packet structure

After 9 bytes of constant preamble, the Proximity UUID, Major and Minor values are transmitted.

UUID is 16 bytes long, Major and Minor are 2 bytes long. Together they form an ID for your iBeacon. Mobile devices recognize which Beacon they approach on the basis of these values.

The final byte is the packet is used to calculate distance from the iBeacon. It represents RSSI value (Received Signal Strength Indication) measured at 1 meter from the iBeacon. The value of this byte changes automatically if the user changes the transmission power for the iBeacon.